Sulfur recovery apparatus



Feb. 23, 1965 F. M. TOWNSEND SULFUR RECOVERY APPARATUS Filed March so, 1959 9 Sheets-Sheet 1 I SWEET, DRY GAS SWEET, DRY GAS SWEET, DRY GAS R T O m m m w. 2 mmm 0 2 R 3 S mmmtmmmq 2 6 w w I 3 0G s F 2 m 0 W T R S C E D A U m 2 M M m a S /L f mmmmomm 6 w I 2 G F m A T A w m m w 8 W. s w Eamon? u g 9 k 2 2 m s G T R M 1 Mm s F E M R SOLVENT 8 SULFUR SOLVENT 8 SULFUR SOLVENT 8 SULFUR SWEET, DRY GAS M T 2 0 i 5 m m s w F m M ll Emmommq a m T N E S E W M 2 W 3 .w m s 2 l E. Emmommq T & E T R w m R s CDE s AMM 0 E M S R s T 4 5 Mm 2/ 21 m nmlll 35 m L 0w m m R V0. 6 R T R U C 2 05 F AMX w a i mmmmow m w T m 6 m Rs s V II UA I 4 m we F. s "m SOLVENT 8 SULFUR A TTORNE YS Feb. 23, 1965 i F. M. TOWNSEND 3,170,765

SULFUR RECOVERY APPARATUS Filed March 50, 1959 9 Sheets-Sheet 2 GAS TO GAS T0 ABSORBER ABSORBER "-I M25501? F, 6 MIXER\. 23- AND so:

see SOUR MELTING a 23 SETTLING TANK 6A5 GLYCOL T0 REcoNcEN'TN 28 c::::: S HEAT GLYCOL TO RE- CONCENTRATION '28 645 To MELTING AND AND LIQUID I LI UID MXER SULFUR GLYCOL SUEFUR F I G. 8 a so A SOUR -23 GAS /REACTOR AND MDfER GLYCOL T0 RECONCEN'TN r HEAT F I G 7 l 90% GLYCOL H20 56 57 k DRY 2 F I G. STEAM v55 40 2 9 PREHEATER 69 55 3 REFLUX 39 T COOLING WATER 64 sucor. 52 Q STORAGE a SURGE TANK t 44 I 0. 53 as H E GLYCOL H H 3 5., 37 PUMP Q REBOILER b 35 w -E 7 A 34 36 58 STORAGE LIQUID IN V EN TOR. SULFUR FRANCIS M. TOWNSEND 72 W, A M,%%Aw awn A1 ATTORNE Y8 Feb. 23, 1965 F. M. TOWNSEND SULFUR RECOVERYAPFARATUS 9 Sheets-Sheet 3 Filed March 30, 1959 3305 $53 D m k m M E ET m M 7m r m w w m w: W O [Y T w: M. 1 m: s qfizwuz m m :1 N! M R W QNZQDQ PM" 3 3' F .553 M t :5 m RT 2? NS r W! mmiommm 55:3 \I M s m m V 8 V s a N" z o S W 0 v2 3 w 53: N a 585m z m Feb. 23, 1965 F. M. TOWNSEND SULFUR RECOVERY APPARATUS 9 Sheets-Sheet 5 Filed March 30, 1959 tommmtliou t2 Own 1 wbsmmt m w tmztbm h tmztpm 0h tam Sm 1N VEN TOR.

FRANCIS M. TOWNSEND Emmommw om (8.

mmbmmmmm 16 5 mom m smmm \Eq Ema ATTORNEYS Feb. 23, 1965 F. M. TOWNSEND summ RECOVERY APPARATUS 9 Sheets-Sheet 6 Filed March 30, 1959 F V R s .545 26 E3 m M M '17 0 E en mm LA 6 m m I v V mm mm 2% 9n E... N

t2 0mm @I' 0 M n n 'kbkdbm F Y mum En Tu 32 B m3 5m 8m 33: 3?.IIJ. nfiunnuflvui uu... 0mm owe ran... mqm QMXE f m mm mm tmm 6. @553 men g M mm J 535m mm LA 62 W 8 mwm no Emmommq ow we Em 8m m4 \l 26 his ATTORNEYS Feb. 23, 1965 F. M. TOWNSEND 3,170,766

summ RECOVERY APPARATUS Filed March 30, 1959 9 Sheets-Sheet 7 DRY GAS 305 FIG. I4

307 SETTLER INVENTOR. F I G l5 FRANCIS M. TOWNSEND ATTORNEYS Feb. 23, 1965 F. M. TOWNSEND SULFUR RECOVERY APPARATUS 9 Sheets-Sheet 9 Filed March 30, 1959 mm 8m 0% 8% mmm mmm mmm m Rn m NR H "mmfihmm w in 0mm m mwn m8 6m 2m km 0% 38 mum New on Rm mwm mum in wow new 8m 58 25.: wmn 8n mmn mm 8. mun van an Sm NN 8n Rm n5 LES 3w mom man man an .I no .55 m3 R m Own Q83 own mmn N z L 50 vi A :n

WQQ .wm qm hmmkm xmm ,WZZAM ATTORNEYS United States Patent 3,176,766 SULFUR nncovnnr ArrAnA'rUs FrancisM-ark Townsend, Norman, Okla, assignor to Laurence S. Reid, Norman, Dinar Filed Mar. 30, 1959, Ser-No. 302,980 8 Claims. (U. 23-263) The invention relates to apparatus forthe recovery of sulfur, the sulfur content'of the hydrogensulfide.

Numerous workers in this art have investigated the basic method for recovering sulfur from hydrogen sulfide, according to the 'equationsrf 3,170,766 Patented Feb. 23,

ers are installed in series with sulfur condensers and a 1 gas re-heater between chambers. In this instance the minimum economic capacity is about 25 tons of, elemental sulfur per day. 7

The. object of thisinvention is to provide a more efficient, and less expensive, single-stage apparatus for the recovery of elemental sulfur from gases containing hydro gen sulfide, which apparatus will have a relatively low minimum economic capacity in terms of tons of elemental sulfur per day. i Y t A further object of the invention is to provide new equipment for the reaction between-hydrogen sulfide and sulfur dioxide in which the sulfur produced by the reaction is formed rapidly and in such particle size as to be readily recoverable.

Another object of the invention is to provid apparatus for the simultaneous dehydration and desulfurization of sour gas and for the recovery of elemental sulfur therefrom.

Until this invention no process or equipment has been developed to'use thesebasicreactions which is economically attractive for;relatively'smallscale production,-or for removing the hydrogen sulfide: from gases in which it was present only in minute amounts;

This application is a continuation-impart of-my 'copending application'Serial No 587,991, filed May 29', 1956 .(now. Patent No. 2,881,047, dated April 7,1959), which is a continuation impart of my prior application,-Serial No. 392,650;- filed November17, 1953, now abandoned.

, gaseous mixture containing hydrogen sulfide, is sweetened .by flowing it-in intimate contact with a solutionofsulfur.

The Claus process, for example -makesuse of these reacts withthe hydrogen sulfide'and carbon dioxide com- 'ponents of the gas mixture and effects their removal.

These acid gases are then released from the amine solution drogen sulfide from naturalgasand other gases.

from natural gas. 2 V t ,7 These and other objects of the invention are accomplished by apparatus in which the sour gas','rneaning' any dioxide in a concentrated aqueous solution-of-a neutral, inert,- stable, organictsolvent'having a vapor pr'essure at 20 C. of not more than about millimeters of mercury and wherein the solubility of water'intheorga nic solvent is at least about 2% by weight at C."andlpreferably not: less than about 5% by weight at 20". C. The aqueous; solution ofthe organic solvent acts bothas acatalyst and i as a medium'for the reaction between'hydrogen sulfide by heat. In the Clauseprocess, onerthird of; this acid gas mixture is separatedland oxidized to form-the propen amount of sulfur dioxide to enter intothe reaction 'inithe equations above The remaining hydrogen sulfideandthis I sulfur dioxideare then combine'd'and the reaction between them is catalyzedby their passagethrough a bed of bauxite; The reaction temperature during passaeethrough the catalyst issufficiently high that the sulfur formed by the reaction remains in vapor form. The sulfur vapors arethen c'ondensed, recovered, and. stored in liquid or solidstate, -While this process looks attractive 'froma theoretical standpoint, it has many undesirable features as'a cornmercialprockess. For example, the amine absorption pi'ocess'for removing hydrogen sulfide from th feed gas requires a relatively high capital investment, and entails fhi gh maintenance costs, due to. corrosion, particularly 'wherecarbon-dioxide is present in the feed gas'inappre ciable percentages and is absorbed by theamine solutions, along with the hydrogen sulfide, and liberated as carbonic acid. 'In many-instances, the carbon dioxide content of the acidgas mixture is sogre'at that isimpossible to oxidize thisgas tojproduce the sulfur. dioxide requirement without adding substantial amounts of natural gas to'fo rm v a combustible mixture.- Usually, the addition .of this, hydrocarbon gas causes carbon deposition onthe catalyst,"

t reducing its ellectiveness, progressively' to the point where it becomes inoperative; The minimum economic capacity for a plant'of this typegwith a single eatalyst chamber is from 8 to 10 tons of elemental sulfur-penday. Where a higher'recovery eificiency'is desired, twov catalyst chamand sulfur dioxide. 1 I A neous, and particles of sulfura're formed and dispersed in the solution. These particles may be easily separated from v the aqueous organiclvsolvent tofreinoveiand'to recover elemental sulfur.

The fundamental reaction of the'invention may be demonstrated on a laboratory scale by dissolving sulfur dioxide in a concentrated aqueous'solu tion oftriethylene glycol, for example, until a' distinct yellow color is ob tained. ;If hydrogen sulfide, from the reaction of a strong 7 acid and sodium sulfide, isthen; passed through the-sein tion, a cloudy dispersion of precipitated'sulfur forms irn recoverable.

mediately. Upon standing the sulfur will settle and-iisi The basic innovation which-thesuccess ofthis invention depends is theme of apparatus in jwhich'a concentrated, aqueous solutionof an organic solvent having tlie properties set'forth above, is the reaction medium.

Any neutral, stable, inert organic solvent-having the specified vapor pressure and solubility properties may be" used, so long as the organic solvent contains at least two heteroatoms (i.e., atoms'of elementsother than hydrogen 7 and carbon), atleastone of which. isa lower chalcogen such as oxygen or sulfur, andso long as the number of; vicinyl hydroxyl radicals does not'exceed .two.. -Theheteroatoms appear necessary to provide sufficient solubility ofsufur dioxide in the'organicsolvents. Solvents 5 with three or more vicinyl hydroxyl groups are unsatis factory, due to instability anddecomposition. With aque:

'ous solutions 'of solvents within the class defined above,

which are preferably atileast byweight organic ma- 'terial, 'thereaction between hydrogen sulfide and sulfur dioxide takes place immediately. Lower concentrations of organic solvents may be employed but reaction rate is usually slower and theioverall efiicien'cy of the Still another object of the invention is to provide equipvment'for the elfective removal of smallquantities of hy- The reaction is virtually instanta 1 process may be correspondingly diminished unless this effect is compensated by more expensive modifications in process equipment and operation. The preferred concentration of organic solvent in water solution entering an absorber is about 96 to 99% by weight. The small amount of water present in the concentrated solution exercises its well-known catalytic effect on the reaction. However, the absorption by the organic solvents of the water produced by the reaction and the water absorbed from the inlet sour gas stream causes immediate diminution of the effect of such water upon the reactionrate insofar as there is any tendency for the presence of excess water to prevent the reaction from going to completion. In this respect, the solvents ofthe type defined above actualy aidthe reaction and force it to completion by removing one of the products, water, as it is formed.

Among the organic solvents which can be used in the process of this invention are the following:

Mercaptoethanol Tetrahydropyran-Z-methanol Ethylene glycol Diethylene glycol Triethylene glycol Tetraethylene glycol 3-thiapentanediol-1,S (thiodiglycol) Propylene glycol Dipropylene glycol 3-methylpentanediol-1,5

Pentanediol-1,5

2-ethylhexanediol-1,3

Hexylene glycol Octylene glycol 2-ethoxyrnethyl-2,4-dimethyl-pentanediol-l,5 2-methoxymethyl-2,4-dimethyl-pentanediol-l,5 2-methoxyethyl acetate 2-ethoxyethyl acetate 2- (2-ethoxyethoxy) ethyl acetate 2- Z-butoxyethoxy) ethyl acetate Triethylene glycol monomethyl ether acetate Ethylene glycol diacetate Diethylene glycol diacetate Di Z-methoxyethyl) male ate Propylene carbonate Diacetone alcohol Acetonylacetone Diethylene glycol diethyl'ether Ethylene glycol monomethyl ether Ethylene glycol monoethyl ether Ethylene glycol monobutyl ether 2-ethylbutyl 2-hydroxyethyl ether Ethylene glycol mono-n-hexyl ether Diethylene glycol monomethyl ether Diethylene glycol rnonoethyl ether Diethylene glycol monobutyl ether Triethylene glycol monoethyl ether Diethylene glycol mono-n-hexyl ether Tetraethylene glycol dibutyl ether Ethylene chlorhydrin Propylene chlorhydrin Polyethylene glycol chloride of molecular weight from 90 to 210 a-Methylbenzyl 2-hydroxyethyl ether Diethylene glycol monophenyl ether 3-methoxybutanol 1,3-b utylene glycol 1,4-butanediol ascending sour gas.

FIG. 2 is a flow diagram of a modified sweetening process and apparatus;

FIG. 3 is a flow diagram of another modification;

FIG. 4 is a flow diagram of a fourth modification;

FIG. 5 is a fiow diagram of a fifth modification of a sweetening process and apparatus in accordance with this invention;

FIG. 6 is a flow diagram illustrating a method and apparatus for recovering elemental sulfur from a sweetening process;

FIG. 7 is a flow diagram of another sulfur recovery method and apparatus;

FIG. 8 is a fiow diagram illustrating the sulfur recovery method of FIG. 7 with modified apparatus;

FIG. 9 is a flow diagram of a complete sweetening and sulfur recovery process and apparatus; A

FIG. 10 is a flow diagram of another complete sweetening and sulfur recovery procedure and apparatus in accordance with this invention;

FIG. 11 is a flow diagram of a complete sulfur recovery process for treating gas containing a high proportion of carbon dioxide and a relatively small proportion of hydrogen sulfide wherein the residue gas is relatively worthless and is vented;

FIG. 12 is a flow diagram of aprocess and apparatus for sweetening and dehydrating gas for pipeline sale;

FIG. 13 is a flow diagram 'of a process and apparatus for recovering sulfur from acid. gases produced by an amine-type sweetening plant; 7

FIG. 14 is a fiow diagram of aprocess and apparatus for recovery of sulfur from gas in accordance with this invention, with provision to retain all sulfur dioxide in the system;

FIG. 15 is a'modification of the apparatus of FIG. 14;

FIG. 16 is a flow diagram of a'process and apparatus for recovery of sulfur and nitrogen from a gas containing these compounds;

FIG. 17 is a flow diagram of a modified process and from a gas containing the same.

' q The apparatus of this invention is very flexible and may be operated with several variations. The sulfur dioxide may be pumped and dispersed into the sour gas entering the reactor, there to be contacted by and absorbed in a descending stream of aqueous solution of organic solvent. Or the sulfur dioxide may be introduced into the reactor at a point substantially below the concentrated organic solvent solution inlet, there tomix and react with the Or the sulfur dioxide may first be dissolved in a portion of the total stream of organic solvent and thenpumped into the reactor at a point substantially below the inlet of the remaining portion of the organic solvent solution. Regardless of the procedure and apparatus selected, the reaction takes place immediately and elemental sulfur is precipitated and dispersed in the descending solution. I

Sulfur dioxide is soluble in aqueous, concentrated solu tions of the organic solvents of the class defined herein.

[ the solubility is such that sulfur dioxide may be substantially stripped from a carrier gas by contacting it with a concentrated, sulfur dioxide-free aqueous solution of such an organic solvent in a counter current absorber. However, for best results, the concentration of sulfur dioxide in the solution should be restricted to 10% by weight, or less, in order to minimize the vapor pressure of the sulfur dioxide solution and possible resulting losses of sulfur dioxide due to its tendency to vaporize and escape.

The reaction between sulfurdioxide and hydrogen sulfide in an aqueous organic solvent can be conducted in a variety of ways andin a variety'of equipment. One method is illustrated in FIG. 1 of the attached drawings, wherein the sulfur dioxide-free organic solvent solution, which may be a regenerated, recycled solution, is split into two portions. One portion ,of this solution is introduced into the top of a sulfur dioxide absorber 22, there rial in the still 24.

. meanwhile into the reactor methods recited above.

. I to effect recovery of this component from'the residuegas. I The sulfur dioxide required for the reaction with hydrogen sulfide is added to the remaining portion of the organic solvent and this stream is introduced' intothe top of areactor 23 where it joins the sulfur dioxide-laden solvent) from the absorber, 22 and effects the reactionlbetween hydrogenisulfide and sulfur dioxide to produce elemental sulfur I I A second design is shown. in FIG. 2. All of the "concentrated sulfur dioxide-free organic solventis introduced into the top of a sulfur dioxide absorber 22, there to effect recovery of this component from, the residue gas. Liquid sulfur dioxide is pumped intothe top of a reactorI23 where it 4 mixes with sulfur dioxide-laden organic solvent from the absorber '22. The resulting sulfur dioxide-solventmixture descends through the-reactor 23 and contacts the [ascending sour gas, thereby effecting reaction, between hydrogen sulfide and the sulfur; dioxide A third modification isillustratedyin'FIG. 3, wherein the required quantity of sulfur dioxide, in either vapor or liquid form as required, is added to the stream of sour gas entering a reactor 23, and the entire stream of concentrated sulfur dioxide-free organic solvent is introduced 7 into the top of a sulfur dioxide absorber 22, there to 7 .recover an excess of this component from the residue gas.

The sulfur dioxide-laden solvent issuing from the absorber 22 is introduced into the top o'f the reactor 23 to effect- I the reaction between the hydrogen sulfide and the sulfur dioxide. I t i A fourth method and apparatus forthis invention is shown in FIG. 4', wherein sulfur dioxide-free organic solvent is introduced into. the top of a sulfur dioxide ab sorber'22, there to recover the excess of, this component from the residue gas. The sulfur dioxide-rich solvent is removed from the absorber 22 and heated in a still 24 and a reboiler 25 to'strip the volatile components, including the sulfur dioxide, from the solvent. If the sour gas contains 'mercaptans, these are taken up by the organic solvent-in the absorber 22 and stripped as volatile mate- The reconcentrated solvent is cooled in a heat exchanger 26 and pumped back to the top of the sulfur" dioxide absorber 22, thus completing the cycle.

for conducting the sweetening reaction I prised of the two separate superimposedassembly may be two separate vessels connected by suitable piping permitting gravity flow of the solvent from the absorber to the reactor,or the two vessels-may be set on a common elevation and the transfer of solvent from the absorber to the reactor may beeffected by pumping through suitable, connecting piping.

. The reaction between hydrogen sulfide and sulfur dioxide is exothermic and, in any, of the preferred forms of the invention listed above, the temperature rise in the reactor due, to heatpf the reaction may be limited and/or controlled if desired. For example, the extent of the temperature rise, based on sour gas entering the reactor at 80'F,, contacting 98% diethylene glycol and sulfur dioxide as solvent entering the reactor at 100 F.,-and solvent concentration atthe reactor outlet reduced to 95% by weight, is listed as follows. 7

Percent H 8 in gas: 20 1 Max. reactor temperature 10 a 202 V; 40 j i 226- I If'solvent concentration is decreased below 95 percent by weight, resulting from decreasing the quantity of solvent charged, the maximum proportionately.

I FIG. 6 is a flow diagram of one of thepreferre'd designs for effecting separation of the elemental sulfur from the. v

solvent, comprising means for maintaining the temperature of a reactor 23 inithe range l00-150 F., forexampie, by vuse of react-or intercoolers (not shown'),. means for discharging the sulfur-laden slurry from the'base of the reactor 23 to arsulfur heating and settling tank '28, means for applyingheat to said tank- 28 in quantity sufficient tojcontrol theternperature of its contents in the range 250-275 F., means for agglomerating and melting the sulfur particles, and'eifecting separation of Asecond separate stream of the same( onadifferent) sul fur dioxide-free solvent is'used to effect solution of the sulfur dioxidetstripped from the first solution above and introduced into the top' of areactor 23 to effect reaction between hydrogen sulfide and sulfur dioxide, the remainder of the required sulfu rfdioxidebeingintroduced. I

23 by any one of the three A fifth design, shown in FIG. 5, comprises means for iintroducing therequired amount of sulfur dioxide-free concentrated organic solvent into the top of a first sulfur dioxideabsorber 22, there to recover the excess of this component from the residue gas, whichquantity may be substantially all or only a portion of. the total solvent requirement for the process, means for removing said sulfur dioxide-enriched solvent from the bottom of the first absorber 22 and introducing it into'a secondsulfur dioxide absorber 27 to eifect solution of any additional sulfur dioxide required in the reaction, means forpumping the required quantity of the same sulfur dioxide-free solvent to the top of the secondab'sorber 27 to effect It is-apparent that inthe foregoing descriptions the sulfur dioxide absorber 212may1-be superimposed on top, of the reactor. 23, either as a single pressure vessel comthe slurry into a molten sulfur. phaseland an aqueous organic solventphase, means for discharging the sulfur 'from the bottom ofthe settling tankv28 to storage or to a sulfur burner (not shown) as required, means for discharging the solvent to a'still (not shown) for reconcentr ation, and mean'sfor discharging the sulfur dioxidevaporsstripped from the slurry into the reactor 23 or into a sulfur dioxide absorber (not shown) for recovery and reuse by solutionin the concentrated solvcnh Another embodiment of apparatus for separating elemental sulfur from the solvent is illustrated in FIGS. 7 and 8, and comprises means for maintaining the reactor temperature in the desired range, meansfor. flowing the sulfur-laden slurry from the base of a reactor 23 by gravity into a sulfur melting and settling tank 28 which is connected to the reactor 23 by means of liquid and vapor flow and equalizing conduits (not shown) so that the two vessels operate at the same pressure, means for applying heat to the settling tank, 28 in quantity sufficient to maintain the temperature ofits contents in the range 250-275 F., means for agglomerating andmelting the sulfur particles and effecting separation'of the slurry into a molten sulfur phase and an aqueous'organic "solvent phase, means for discharging. the sulfur from the bottom of: the tank 28' to storage or to asulfur burner (not shown) as required, means for discharging the organics'olvent to a still (not shown) for reconcentration, and means for discharging the sulfur dioxide stripped from the slurry back, to the reactor 23 for use '28 may operate at the same or difie'rent pressures. anticipated that the reactor 23 shall operate at any pressure required by the gas system it serves, but the sulfur in that zone It will be understoodlthat in the above descriptions the reactor 23 and the sulfur melting and settling drum It is melting and settling drum 28 may operate at the same pressure or at a lower pressure, such :as from l0 to and distinct sections, 01 1116 temperatures will increase 30 p.s.i.g., which pressure will be adequate to supply the necessary driving force to deliver the various streams to the desired points.

In the second arrangement discussed above for separating elemental sulfur, the sulfur i melting and settling drum 28 can be an integral part of the reactor 23 if the capacity of the lower'portion of that vessel is of adequate size, or the react-or23 can be erected in avertically disposed position at the center of the horizontally disposed melting and settling tank 28 with both vertical and horizontal portions fabricated into a single vessel, or the reactor 23 and the melting and settling tank 28 can be two separate vessels properly "melting and settling drum 23, and a second line to deliver A located With respect to each other'and connected with a lower' line to deliver slurry from the reactor 23 to the .stripped sulfur dioxide vapors from the settling drum on the particular organic solvent employed and the extent of reconcentration desired. Excess water passes overhead in the vapor form. The vapor may be cooled and the water condensed and removed from the system. The reconcentrated solution of organic solvent is withdrawn from the bottom of the still, cooled by heat exchange and pumped back to the absorber, thereby constituting f a continuous process.

- sour gas is supplied via an inlet 361. The sour gas The apparatus shown in mosaic 11, inclusive, is described in-detail in the examples which follow.

In FIG. 12 there is shown a reactor 3% to which rises through the gas-liquid contacting devices of the reactor 3% countercurrent to a downward flow of orof 250'275 F. by a heating means (not shown). heating of the slurry strips off excess sulfur dioxide :from

reactor 3%. The slurry of sulfur and dilute organic solvent which collects at the base of the reactor 3G0'is conducted to a settling tank 366 and in the settling tank 33% the mixture is heated to a temperature in the range The the solution and this is returned to the bottom of the reactor 3% via a line 338. The sulfur particles in the sulfur settler 3% are melted and liquid sulfur which collects near the bottom of the settler 3G6 is removed via a line 3 5? and a control valve 310. Part of the sulrur is Withdrawn to storage via a line 311 and part of it is conducted to a burner 312 via a line 313. The

' concentration or" greater.

organic solvent is decanted from the sulfur settler 366 7 via a line 314 and a valve 315 controlled by a controller 316.

through line 317 and through a heat exchanger 313 -where'-it is heated. From the heat exchanger 318 it passes via a line 319'. into-a solvent' still 329 where the excess of water is removed by evaporation from the solvent and the latter is concentrated to about 98% The water is discharged from thestill .32 3 via a vent'32l. As the glycol descends the still'32t it becomes more concentrated as the temperature rises and excess water is vaporized and removed.

At the base of the still 320, the solvent is heated by a 'reboiler 322 to a temperature corresponding to the ganic solvent solution, for instance, a solution of sulfur dioxide in 98% triethylene glycol. In this apparatus, in addition to the removal of sulfur from sour gas, water is removed to produce sweet dehydrated residue gas for pipeline sale. The sour gas enters the lower portion of the reactor 300 at line pressureand atmospheric temperature. The solution of sulfur dioxide in organic solvent is pumped into the top of the reactor via a line Upon contact between the sour gas and the sulfur dioxide in the presence of the organic solvent, reaction occurs forming sulfur and water. Sulfur is insoluble in the organic solvent but the water is absorbed. The amount of solvent supplied to the reactor 399 is in sufficient quantity so that the water concentration increases to only about 5% of the weight of the glycol upon absorbing all the water produced by the reaction and absorbing all of the water vapor content of the inlet gas.l The sweetened gas from which the hydrogen sulfide and water have been removed rises from the reactor 36%) into the high pressure sulfur dioxide absorber 393 where it iscont'acted by a descending stream of concentrated (preferably at least 98%) organic solventtfree of sulfur dioxide) which is introduced to the absorber 303 via an inlet 304 near the top thereof. The concentrated-solvent absorbs any excess of sulfur dioxide remaining in the sweetened gas and any traces of water therein and passes downward into the reactor 300. Sweet dry residue gas passes from the top of the absorber 363 via line 335.

The exothermic reaction and the counterflow design of the reactor 300 combined to produce a temperature gradient in this vessel which increases toward the base thereof, thereby providing a rate of reaction which is highest at the relatively hot base of he reactor 3%,

while complete conversion of the hydrogen sulfide tosulfur is accomplished in the cooler upper portion of the I to incoming solvent.

- solvent is stored and withdrawn as needed. the surge tank 327 is impelled by a pump 328 and passes absorber 331.

desired concentration of solvent at the column pressure.

.The solvent is then discharged from the still 320 via a line 323 to the heat exchanger 318 where heat is released e solvent passed through a pump 325, line32d, and cooler 324 to a surge tank 327 where Solvent from through line-3% to the top of the high pressure absorber 363. Another portion of the solvent is removed from the surge tank 327 via a pump 32% andpasses through a line 330 to the top of a low pressurersulfur'dioxide In the low pressure absorber 331 the concentrated solvent descends the column countercurrent to a stream of sulfur dioxide containing gas which enters through line 332 connecting near the bottom of absorber 331. The sulfur dioxide which enters the absorber 331 is produced in the'sulfur burner 312 which is provided .with compressed air from a compressor 336 which is passed into the sulfur burner 312 via the line 335. The sulfur is oxidized to sulfur dioxide in the burner 312 and the heat of combustion of the sulfur in the burner 3l2=rnaybe used to produce steam which can be drawn off for other uses via a line 337. Combustion gas from the burner 312 passes via a line 333 to a cooler 339 -;and a heat exchanger 34th from which it passes via a line 332into the bottom of the low pressure absorber 331. The gas containing sulfur dioxide passes upward in the absorber 331 where it is contacted with and absorbed by the concentrated glycol solvent which descends therein. The waste residue gas passes out through a vent 3 81 at the top of absorber 331. The organic solvent containing sulfur dioxidecollects near the bottom of the absorber 331 and is drawn off via an outlet 345 where it passes through a pump 346 and a line 3% into the reactor 3%.

347 to the inlet The apparatus shown in FIG. 12 has the advantage that sulfur dioxide can be lost at but three points. One point is that at the top of the high pressure absorber 3&3. Another point is that at the vent 341 at the top of low pressure absorber 331 and the third point is atthe vent 321 at thet'op of the glycol still 320. It is apparent from FIG. 12 that very high recovery efficiency for sulfur may be obtained with this design.

FIG. 13 shows an apparatus which may be employed to recover suifur from sour gases produced by an aminetype sweetening plant. Referring to this figure it is seen that the sour gas stream enters the system through a line 356 and is divided into two portions by a three-way valve This organic solvent containing water passes" sulfur storage.

' in the settler 3% is evaporated and passes out of the sul fide of the sourgas. s V

tler'306 is drawnolf via a line and a pump361, through a heat exchanger 362 where heat is absorbed glycol passing through thecoiffnfida gas stream passes via a-- line 352 to a line 353 where the v 351, One portion comprising one' third of the total acid I acid gas is-admixed witha stream of air from a compressor 356. The mixture of airand acid gas in line 353 passes into a burner and boiler 354'where the hydrogen-sulfide of the acid gasis ox-idizedto sulfur dioxide.

gas temperature is reduced to 120 to 130 E.) and a line 357 to rejointhe main portion of acid gas stream which passes from the three-way valve 351 via a line 301 to the lower part of a reactor 30f) where it ascends coun- -tercurrent to a stream of concentrated organic solvent which enters the reactor 3%. throughan absorber 303.

The hydrogen sulfide and sulfurdioxide in the mixed gas The gas streamicontaining the sulfur dioxide thus pro duced passes through a line 355,a cooler 356 (where the stream which enters the reactor Sttb'via line 3tllreact in the presence of the organic solvent in the' reactor 3%, thereby producing sulfur and water, the latter being ab sorbed by the organic solvent. The inert portions of the gas stream pass up through the absorber 3% Where they are contacted with fresh concentrated organic solvent and [any remaining traces of sulfur dioxide are removedby the solvent.

Thereafter the. inert gas is discharged via a vent 305. nConcentrated solvent enters'the absorber 303 via an inlet 364 near the upper part thereof and passes downward to the reactor 3%. Sulfur formed by the reaction of hydrogen sulfide with sulfur dioxide collects near the bottom of the reactor 36%) and is drawn.

oif as a slurry with solvent through a line 337 leading to a sulfur settler 306. The slurry inethe sulfur settler 306 is maintained at a temperature of 250 to 275 F. by means i of a closed heatingcoil Sda to which hot solvent is suppliedvia lines 3t6b and 366a connected to a solvent still 7 p 320. At a'temperature of 250 to 275 F the sulfur in the sulfur settler 3% is molten and may :be withdrawn in liquid form via-a line 3&9 and acontrol valve 310 to Any sulfur dioxide in the organic solvent fur settler 3%. via a line 398 whence it is returned to the reactor 3% for further reaction with the hydrogen sul Dilute solvent from the sulfur setfrom freshly concentratedsolvent passing through the heat exchanger from the still 325). The dilute solvent separator 377. Uncondensed gases and w some water] vapor are discharged via' a vent 378, While condensed water collects near the x-bottom, of the separator 377 where it is withdrawn via a line 379'-and a pump 380 from I whence'it passes via a line 381 bac l to the top of the still 32ttasreflux. A controller 382 regulates agvalve 383 to discharge excess water from the system thro'ugh the line-38,4." I v v I-n-the apparatus of FIG. 13 it is important to note'that by splitting the acid gas stream into two portions, one ,being one-half as great as the other, passing the smallerv portion to the burner and boiler 354 for oxidation with "air and then returning the oxidized-gas streamcontaining sulfur dioxide back to 'join the'larger stream of acid gas,

there is thus obtained the stoichiometric proportions of hydrogen sulfide and sulfur dioxide required for the-complete reaction of these materials to produceisulfur'and water. In this way the appropriate amount of sulfur dioxide required for the complete conversion of thesulfur dioxide is retained in and recycled between the reactor 3M) and the absorber 303. This is a feature which substantially contributes to the improvement 'ofithe sulfurrecovery efficiency since excess sulfur dioxide required for complete reaction is retained in the system at alltimes. I If the acid 'FIG. 13 contains a high content of carbon dioxide so that .boiler 354, then hydrocarbon gas, eithersweet or sour,

may be mixed with the acid gas supplied to the burner 354 in a quantity sufficient to insure'combustion.

FIG. 14 illustrates-a modification of the apparatus which is particularly adaptableto natural gas. This sysfrom the exchanger 362 passes via a line 363 to a glycol still 320 where the solventis concentrated by boiling off most of the water to raise the solvent to a suitable concentration, preferably at-least 98%. Concentrated hot solvent collects near the bottom of the. still 320 and is withdrawn via an outlet 323; At a T 365 the hot solvent stream is divided and part passes via the line 30% through the closed coil 306:: in the-sulfur settler 3% to supply heat to' the latter. This solvent then passes via the line 3060 to'a line 366 Where it passes through the- 1 heat exchanger 362 and then via a line-367 and a pump 368 to a cooler 369 where its temperature is lowered tothe proper temperature for reaction. From the cooler 369 it passes via the line same the absorber 303. The

valve 374} in the line 366 controls the relative quantityof to the heat'exchanger 362;

Returning now to the hydrogen sulfide burner 354,

wherein the hydrogen sulfide contained in one-thirdof the. acid gas stream is oxidized with air; the heat from the burner may be used to generate process stearn or used to and passing directly taining sulfur dioxide which is introduced through an inlet 302; The hydrogen sulfide is removedbyreaction' with the sulfur dioxide-and the'sweetened gas stream passes upward to the absorber section 363 wherein traces of V sulfur dioxide'remaining in the gas stream are removed by a countercurrent stream of solvent. Thesweetened gas passes out of the apparatus via a line 305 and the .solvent enters the absorber via an inlet 304; -,The slurry ofsulfur in dilute solvent is removed from thereactor section 305 from the bottom thereof via a line 307 and a v control valve 307a leading to a low pressure settler. 3%

reconcentrate the organic solvent employed in the process a and apparatus. Steam from the boiler 354 passes via a line 371 to'the-solvent still 320 and the condensate is returned via a line 372. A reboiler 322 is connected to the solvent still 320 to provide. additional heat forevapo ration of the water in the dilute solvent which enters the still via the line 353. The overhead from the solvent? still 320 passes via a line 375 and a condenser 37 to a where molten sulfur is separated as previously described and removed via line 309. The sulfur dioxide isflashed off via a line 390 and a valve 391 leading to low pressure 7 'sulfurdioxide absorber (not shown) wherein the sulfur dioxide gas stream is contacted with concentrated organic solvent which i's then recirculated via anapparatus (not shown) through an inlet 302. The control valve 307a prevents return of sulfur dioxide to the reactor section 306. The solvent is withdrawn from the settler 306 via a line 314 and a control valve 315 whence it passes via a line 317 to a solvent still (not shown). i

' FIG. 15' illustrates another modification ofthe apparatus providing high efficiency of sulfur dioxide recovery. j i

In this figure the reactor section 300 and vthe absorber 1 section 3630f the apparatus are as shown in FIG. 14,t he any difference being that a line 308 leads frornthe settling tank 306 to the reactor section 300 to return sulfur dioxide which is evaporated in the settlertank. .Sour gasenters the system through an inlet'3tl1,; rises through the reactor section 300 and theabsorber section 3 03 and is released for pipeline sale via'a line 305. A solutionof sulfur dioxide in organic solvent is introduced through antinletStlZ and concentrated organic. solvent gas stream supplied to the apparatus of.

oxidation is difficult'or impossible in the burner and.

432 where heat is absorbed.

- passes via aline 433 to a flash tank 434 where the sulfur 314, control valve 315, a line 317, through a heat exchanger 318 where heat is absorbed and via a line 381 to a flash tank 392 where the sulfur dioxide remarmng in the solvent is vaporized and passes out through a line 393- to a low pressure sulfur dioxide absorber 331 where,

along with sulfur dioxide from sulfur burner flue gas, it is absorbed in concentrated organic solvent. The low pressure absorber 331 is connected via suitable tubing and a pump (not shown) to the inlet 302 to reactor section 3% to return solvent and sulfur dioxide to the reaction section. Solvent from the flash tank 392 is removed via a line 3% wherein it passes to a solvent still (as shown in FIG. 12) for reconcentration andrecycling.

Turning now to FIG. 16 there is shown a modified apparatus for removing hydrogen sulfide from a gas streamcontaining a large percentage of inert gas such as nitrogen. This apparatus is applicable to a gas stream containing,

for example, 5% hydrogen sulfide, 7% carbon dioxide, 32% nitrogen and the rest gaseous hydrocarbons, having a low calorific content of 616 B.t.u. per cubic foot. In FIG. 16 the sour gas stream enters a reactor dill-via a line 4% connected near the bottom thereof. The sour gas rises in the reactor 491 contacting a descending current of organic solvent containing sulfur dioxide which enters the reactor 4&1 via a line 492 near the top thereof and connected to the bottom of a high pressure sulfur dioxide absorber 4%. "in the reactor 401 the hydrogen sulfide and sulfur dioxide react to form water and elemental sulfur which descend to the bottom of the reactor ttll'as a slurry with the organic solvent. This slurry is .'ithdrawn via a line 565 and passes through a control valve 4% to a sulfur settler 4-37. In the settler 407 the sulfur is separated from the diluted organic solvent and the sulfur is withdrawn by a line 4% wherein part of itis withdrawn by a valve 4&9 and a line 410 to storage. The remainder of the sulfur is passed via a valve 411 and a line A12 to a liquid sulfur dioxide unit 413.

, The sweetened gas passes from the reactor 401 via a line 4-15 through heat exchangers did and 417 where it is heated and then to an inlet 418 to a nitrogen absorber 419. The gas stream passes upward in the nitrogen absorber 419'whereit, is contacted with a stream of'hot liquid sulfur dioxide which enters near the top of the nitrogen absorber 419 through a line 420. Nitrogen is absorbed by the hot liquid sulfur dioxide and the gas stream free of nitrogen passes out of thenitrogen absorber 4T9 through the top thereofvia a line 421 where it passes through the heat exchanger 416 and releases part of its 1 heat to the gas stream in line 415 and passes then through drogen sulfide, nitrogen and sulfur dioxide removed therefrom and is now suitable for pipeline sale.

Returning now to the sulfur settler 4&7, it is seen that the dilute organic solvent contained therein is withdrawn via a line 43% and a control valve 431 toa heat exchanger Then the warm solvent dioxide contained in the diluted solvent is flashed off at high temperature. The sulfur dioxide leaves the flash tank 434 via a line'435 and the dilute solvent'passes out.

of the flash tank 434- via a line 436, a control valve 4-37 and aline 438 leading to a solvent still 439. In the still 439 exchangers 01 and 562 in line 503.

the water contained in the solvent is evaporated at high temperature and is vented from'the top of the still 439 via a ventline 446; A reboiler 44-1 is connected to the line 449m pump 5% and a cooler heat exchanger 451 to the inlet 425 near the top of high pressure sulfur dioxide absorber 4533.

Turning now to the liquid sulfur dioxide unit 413 which is supplied with sulfur via a line 4-12, it is seen that a stream of air is passed into the unit 413 via an inlet'470 to provide oxygen to oxidize the sulfur to sulfur dioxide. The sulfur dioxide thus formed is iiquified by compression with conventional apparatus (not shown) and the nitrogen and other unabsorbed gases contained in the gas stream are vented via an outlet 371. The liquid sulfur dioxide passes via a line 472 and a pump 473 to a line 474 leading to a liquid sulfur dioxide surge tank 475 where the liquid sulfur dioxide is stored and withdrawn as required bya'pump 4'75 and a line 477 passing through a heat exchanger 478 where heat is absorbed, a line 479 and a second heat exchanger 43% where the liquid sulfur dioxdc is heated with steam to aapropriate temperature. From the last heat exchanger 480 the hot liquid sulfur dioxide passes via a line 428 to the top of the nitrogen absorber 419. Liquid sulfur dioxide containing nitrogen dissolved therein is removed from the bottom of the nitrogen absorber 41? 'via a line 4-35 and a controller 486 through the heat exchanger 478 where heat is released to the liquid sulfur dioxide in the line477. From the heat exchanger 478 the liquid sulfur dioxide containing nitrogen passes via a line 487 to a chiller 48-8 which is connected to a referigerating unit 489 by suitable piping 490 and 491. The chilled stream of sulfur dioxide liquid containing nitrogen passes via a line 452 to a nitrogen flash tank'453 where the nitro 1 453 and leading through a control valve 461 to the liquid sulfur dioxide surge tank 435. Liquid sulfur dioxide is alsorcmoved from the surge tank 435 via a line 462 and a pump 463 where it passes to the reactor 401 and enters through an inlet 45-fconnected near the top thereof. The sulfur dioxide which enters the reactor 401 via the inlet 464 is so controlled as to provide additional sulfur dioxide as may be required to supplement that entering the reactor via the line 402.

In the sulfur settler 407' the temperature of the slurry ofsulfur in dilute solvent is adjusted to 250 to 275 F. and excess sulfur dioxide in the slurry is stripped out in the settler 4&7 and passes via a line'495 which connects with the line 435 and conducts this excess of sulfur dioxide back tov the liquid sulfur dioxide unit 413 via lines 435 and 456. i

FIG. 17 shows a modification of the apparatus of FIG. 16 in which the reaction of hydrogen sulfide with sulfur dioxide and the absorption of nitrogen by liquid sulfur dioxide is. conducted in the same reactorand absorber. A sour gas stream containing hydrogen sulfide and nitrogen enters the system via an inlet 56%) and passes through heat The hot gas from line 583 enters thereaction vessel 564 near therbottom thereof and is contacted with a hot countercurrent stream .of organic solvent and liquid sulfur dioxide. The purified 7 gas stream leaves thevessel 554 via a line 565 connected to the top thereof and passes'through a heat exchanger 506, a line 507, the heat exchanger 501, a cooler 508;, a line 509 and a line 510 to enter the bottom of a high pres- 7 sure sulfur dioxide absorber 511 where the purified gas ascends countercurrent to a stream of concentrated organic solvent which enters the high pressure absorber 511 via a line 512 connected near the top thereof. The descending stream of organic solvent removes any traces of sulfur dioxide and water which may be in the gas stream and the sweet dry gas stream passes out of the absorber 511 via a line 513. The high pressure absorber 511 is suitably connected by flanges 516 and 517 to intercoolers 514 and 515 to regulate the temperature of the materials in the absorber 511. Concentrated organic solvent containing traces of sulfur dioxide collects near the bottom of the absorber 511 and passes via a line 520 through the heat exchanger 506 and a line 521 to a line 522 which conducts the solvent and sulfur dioxide to the vessel 504 for interaction with the sour gas stream. Near the bottom of the vessel'5tl4 there is collected a slurry of elemental sulfur, diluted organic solvent and liquid sulfur dioxide. The slurry is withdrawn through a line 525 to ,a settler 526 where the sulfur. is separated from the liquid and removed via a line 527. The settler 526 is provided with an Overvflow bafile 526a to aid in separation of sulfur and solvent by decantation. That part of the sulfur dioxide contained in the liquid in the sulfur settler 526 which is vaporized passes out of the sulfur settler 526 via a line 528 through which it is returned to the vessel 504. The diluted solvent and sulfur dioxide in the sulfur settler 526 are removed via a line 530 through a control valve 531 and a line 532 to a heat exchanger 533 where heat is ab- The heated solvent and sorbed from a hot solvent stream. sulfur dioxide then pass through a line 534 to a sulfur dioxide flash tank 535 wherev the mixture is heated to a temperature sufiicie'nt to separate the sulfur dioxide from the solvent. The sulfur dioxide gas passes through a line 536 which connects-to a line 537 leading to a liquid sul fur dioxide unit. The solvent free of sulfur dioxide is removed from the sulfur dioxide flash tank 535 via a line 540, a control valve 541 and a line 542 to a solvent still 543 where the water contained in the solvent is removed by distillation and vented througha line 544. Heat "is supplied tothestill 543 by a reboiler 545. The concentrated organic solvent is-removed from the bottom of the glycol still 543 via aline. 546, afcontrol valve Y547, and

a line 548 to the heat exchanger 543 where heat is released to the dilute solvent passing through lines 532 and 534. v

The cool concentrated solvent is then passed via -a line 549 to a solvent surge tank 556 wheresolvent is stored for withdrawal as required. Solvent is removed from the surge tank 550 via a pump 556 and lines 555 and 557, connecting to theinlet 512 on thehi h pressure sulfur dioxide absorber 511. a

Part of the mixture of dilute'oi' ganic solvent and sulfur dioxide which is removed from'the sulfur settler 526 via the line 53% passes through line 56iha heat exchanger 561 and a line 562 to a chiller 563 connected to a suitable refrigeration unit 564 via lines 555 and 566. A chilled mixture of solvent and sulfur dioxide passes from the chiller 563 via a line 567 to a high pressure fiashtank 568. The

vented nitrogen containing some sulfur dioxide vapor then passes via a line 569 and a control valve 576 to a line 571 which connects with line 537 leading to the liquid sulfur dioxide unit. Solvent from the bottom of the tank 568 is removed via a line 575 and a control valve '71 to a line 572 leading to the heat exchanger56l wherein heat is extracted from the solvent sulfur dioxide mixture entering from thelin e 569. From the heat exchanger 571 the solvent passes via a line 575 to a surge tank 576 where the glycol is stored and withdrawn via a line 577; a'pump 578, a line 579-through a heat exchanger 530 wherein steam is used to-impart heat to the solvent which then passes via aline SSIlto a line SSZ lea ding to an inletShS An alternativeroute is provided via theline 597 to the vessel 5tl4'to provide hot recycle of solvent to the reactor.

liquid sulfur dioxide unit 589 via a vent 591. The liquid sulfur dioxide is then passed via a line 592 to a liquid sulfur dioxide surge tank 593 where the sulfur dioxide is stored and withdrawn as required. The sulfur dioxide is withdrawn through a line 594, a pump 595, and a line 596 leading to the inlet 522 near the top of the vessel 504. which leads to the inlet 583 on the vessel 504.

The liquid sulfur dioxide unit 589 is a conventional unit in which ,the sulfur is oxidized with air tosulfur dioxide and the gases arecooled and compressed to form liquid sulfur dioxide. The non-liquifiablegases, such as nitro- T gen and the inert gases of the atmosphere, are vented.

The followingexamples describe continuous processes which are conducted in apparatus of this invention in commercial operations. These examples are intended solely to illustrate the invention and not to limit it in scope. They are directed to specific materials, conditions and apparatus, but it will be apparent to those skilled in the art that many modifications may be madewithout departing from the invention.

Example 1 Referring now to FIG. 9 of the drawings, sour gas,

'which is usually saturated with water vapor, enters the bottom ofa reactor 31 through an inlet line 32.- The sour gas rises through the gas-liquid contacting devices of the reactor 31 countercurrent' to the downward flow of solvent solution, for example a 98%, triethylene glycol solution. The solvent entersthe reactor 31 through an inlet 39 near the top of the upper, absorbing section of the reactor 31. Sulfur dioxide is admitted to the top of the reactor section 31 through an inlet line 38, located some distance below the solvent'inlet 39. Where a bubble cap tower is employed, this may be from 10 to25 traysbelow the solvent inlet, depending on the extent to which the sulfur dioxide must be removed from the residue gas.

The quantity of sulfur dioxide entering the reactor 31 i should be so regulated that the molar ratio of hydrogen 50:

sulfide to sulfur dioxide in the reactor 31 is slightly less than 2 to 1. A lower ratio may be employed as a safeguard against the escape of anyrhydrogen sulfide in the processed residue gas.

Itwill be observed that .in this embodiment all of the natural gas is in intimate contact with the absorbent, concentrated solution of organic solvent. Consequently, any moisture in the gas is removed'along' with hydrogen sulfide. The gas leaving through theoutlet 42 at the top of the sulfur'dioxide absorber section is therefore dry as well as free'of hydrogen sulfide. The dried and sweetened gas ispreferably passed through dual mist extractors 40 and 41 before leaving the column via the outlet 42 to minimize solvent loss by entrainment.

The dehydrationof the sour'gas and the'chemical re-,

action between the dissolved sulfur dioxide and the rising stream of gas containing hydrogen sulfide takes place at v a controlled temperature, preferably of 200, or less, 'largely in that part of the reactor between the sourvwet gas inlet 32 and the sulfur dioxide inlet 33, denoted as the contact zone 33 in the drawing. Sulfur. particles form in the solvent stream and are carried therein to the bottom or base 34 of the reactor column, whence the slurry g is discharged through the outlet 35, preferably under the control ofwaliquid. level controller 37 and motor valve 36. The organic solvent leaving thefcolumn through 4 peratures.

3,1 so, see

the line 35 is diluted by water absorbed from the sour gas and also by water from the reaction. The solvent concentration may be thereby decreased to about 90% or' lower, although it is preferred that the concentration be held at 95% or higher. In order to remove both the excess Water and the sulfur from the solvent solution, it is next subjected to heating to remove the sulfur, and then to distillation to remove the water.

After leaving the base 34 of the reactor column 31, the dilute solvent is passed via a line 43 through heat exchangers id in order to raise the temperature to about 250 F. and coagulate the suspendedsulfur particles. From the heat exchangers the solvent is discharged through a lined-6 into a sulfur receiver 45. This receiver is heated by'a closed steam coil 47, or other suitable heat source, to a temperature of 250-275" F. The receiver temperature must be controlled with care because molten sulfur becomes very viscous at higher tem- Within this receiver 45', the partially coagulated sulfur settles into the molten sulfur phase which is Withdrawn to'storage through the dis-charge line 43 by means of a valve 49 which is regulated by an interface controller 50. The dilute solvent solution is Withdrawn from the sulfur receiver 45 through a line 51, in substantially sulfur-free condition.

umn 54, it becomes more concentrated as the temperature rises and excess Water is vaporized and removed.

At the base of the column the solvent is heated by a reboiler 58 to the temperature corresponding to the desired concentration at the column pressure, and is then discharged from the column 54 through a line 59, which is preferably regulated by a valve 60 under the control of a liquid level controller 61. This hot, concentrated solutionmay be passed through the previously mentioned heat exchangers 52 and.44,-via the lines shown 62 and 63, in order to conserve thermal energy. The concentrated solvent may now be returned directly to the sulfur dioxide absorber for reuse, after cooling. A solvent storage and surge tank 64 is provided in order to provide for constant operation of the system. Solvent from the heat exchangers id is discharged into the surge tank through a line 65 and/or to pump 67 through a line 68. The requiredquantity of solvent is passed through a pump 67, into a cooler 65 via line '70, and thence to the reactor 31 through the inlet 39, thus completing the cycle. The storage tank 64 is provided with anoutlet valve 66 for withdrawal of solvent directly.

The reaction between the hydrogen sulfide and sulfur dioxide which takes place in the reactor will go forward under a wide range of operatingconditions. For example, the process is not adversely affected, by pressures in therange from atrnospheric pressure to 3000 p.s.i.g., at temperatures as high as 260 F., although the efficlency of the process may be improved if the temperature is regulated Within a range of about 100 F. to about 150 F. As with any chemical process, the operating conditions may be varied to achieve optimum yields. For example, an excess of sulfur dioxide of to over the theoretical amount may be adequate for the treatment of truly sour gases in a reactor of proper design. However, where the sour gas has a low hydrogen sulfide content, on the order of l to 20 grains of hydrogen sulfide per hundred cubic feet,a very substantial excess of sulfur dioxide over the stoichiometric requirement may be necessary for complete sweetening of the gas. Similarly, the organic solvent should be reactivated at temperatures appropriate tothe particular reactor 111.

16 solvent employed. For instance, when diethylene glycol is employed, a reboiler temperature in the range between 320 F. and 350 F. produces good results. When triethylene glycol is employed, the temperature may he between 350 F. and 400 F. These and other optimum operating conditions are either readily determinable from physical data or are obvious to those skilled in the art, once the basic invention is disclosed.

The sulfur dioxide for the reaction may be obtained in a variety of ways. it may be obtained by controlled burning of some of the product sulfur, in which case it may be introduced into the absorber column in either gaseous or liquid form, depending on system pressure requirements. Alternatively, the sulfur dioxide may be pre-dissolved in an organic solvent and may be pumped to the column in the form of a solution. Still another alternative would be to remove a portion of the hydrogen sulfide from the sour gas by the conventional amine reaction, oxidize it, and utilize the sulfur dioxide in the reaction. This last possibility tends to defeat the purposes of the invention to some extent when treating natural gas, but is highly desirable when treating acid gases from an amine-type desulfurizer or natural gases with-high nitrogen or carbon dioxide contents to effect sulfur recovery.

' Example 2 An industrial application of the invention is shown in FIG. 10 of the drawings which disclose a system wherein natural gas, containing 6.5% hydrogen sulfide, is treated at a rate of ten million standard cubic feet per day at a pressure of 500 pounds per square inch to yield 24.5 long tons of sulfur and 9,350M m.c.f. to dry, sweet natural gas for pipeline sale.

Referring to PEG. 10, sour natural gas at a pressure of 500 p.s.i;g. and a temperature of F., enters a reactor 111 via a line 112 and passes upward through the gas-liquid contacting elements of this vessel Where it is contacted by a descending stream of sulfur dioxide dissolved in diethylene glycol monoethyl ether, a-solvent more commonly known as Carbito This solution, at the rate of gallons per minute, carries an excess of sulfur dioxide into the reactor 111 via a line 113 to insure complete reaction of all hydrogen sulfide contained in the inlet gas stream. The reaction between sulfur dioxide and hydrogen sulfide is immediate and complete at the gas-liquid interface and the sulfur formed in the reaction descends the reactor column 111 with the solvent in the form of a slurry. At the rate of flow specified here, the heat of reaction causes the temperature of the reacting mixture to rise to approximately 188 F. prior to accumulating in the base of the At'this latter point, additional heat is applied through a coil 111a in sufficient quantity to in crease the temperature of the slurry to approximately 260 F., at which temperature the sulfur particles coalesce and melt.. Liquid sulfur settles into a lower liquid phase while the solvent forms the upper liquid phase. At 260 -F. any sulfur dioxide remaining in solvent is stripped out and passes upward through the reactor column 111 where it may. react with the sour gas continuously entering the column via the line 17.2, thus forming additional sulfur. Liquid sulfur, free from solvent, is withdrawn from the reactor 111 via a line 114 and passes into storage via a line 115, except for that portion which is directed to the sulfur burner via a line 116. Hot, sulfur-free solvent, which now contains water formed as a product of the reaction, passes atthe rate of 97 gallons per minute from the reactor in via a line 117 and heat exchangers 118 and 11.9 and is discharged into the inlet'of a still column 124) wherein the Water is distilled overhead and discharged from the system via a line 121. The remainder of the solvent is further heated and regenerated in a rebo-iier 122, from which point it is discharged via a line 125, the heat exchanger 17 118 and acooler 124 to aconcentrated solvent storage tank 125 which operates at substantially atmospheric pressure and temperature.

Sour gas rising through the reactor 111 reacts with, and is cooled by, the sulfur dioxide-laden stream of solvent which enters the reactor via the line 113. The hydrogen sulfide free gas passes from the reactorv 111 via a line 126 and a cooler 127 wherein its temperature is reduced to the minimum level attainable with plant cooling water (approximately 95 F.) prior to entering a high pressure (500 p.s.i.g.) sulfur dioxide absorber 128. The gas rises through gas-liquid contacting de- Vices within this column where it is contacted by a downflow of concentrated, sulfur dioxide-free solvent introduced into the absorber 128 from the tank 125 via a pump 129 and a line 130 at the rate of 95 gallons per minute. This concentrated solvent descends the absorber 128, effecting recovery of excess sulfur dioxide and water vapor from the gas and reducing the residual content of this compound to 025 grain per hundred standard cubic feet, or less, as the-sweet, dry residue gas passes from the absorber via a line 131 enroute' to market.

Solvent containing some water and sulfur dioxide in solution accumulates in the base of the absorber 128, whence itis discharged at the rate of about 96 gals/min. via a valve 132 and a line 133 into the upper portion of a low-pressure (approximately p.s.i.g.) sulfur dioxide absorber 134. Descending this column, the solution absorbs the remaining sulfur dioxide requirement from the flue gas entering the absorber 134 via a line 135, and collects'in the bottom of the absorber 134 whence it is discharged at a temperature of about 100 F. to the upper portion of the reactor 111 via a line 136, a pump 137 and the line 113, thus completing the solvent cycle. i

. Approximately one-third of the total liquid sulfur discharged from the bottom of the reactor 111 via the line 114 isdiverted via the heat-jacketed line 116, maintained at a temperature of at least 260 F., to a sulfur burner 138 where it is oxidized with air from a compressor 139 which is connected to'the'burner 138 by a line 140. Hot

entering line 214. The line 214 connects with a line 215 through which compressed air from a compressor 216 passes. The mixture of acid gas and air in the line 215 is introduced into a catalyst chamber 217 where the mixture of gases passes through a hot catalyst bed containing silica, bauxite or aluminum-nickel on pumice at 480-520 F. The amount of air from the compressor 216 is regulated with respect to the amount of hydrogen sulfide in the line 214 so that sufficient oxygen is present via a line 218 through a cooling tower 219 and a line 220 into a reactor 221.

Acid gas is introduced into the reactor 221 by Way of the line 213, which is connected tothe reactor 221 adjacent the line 220 carrying'the stream of sulfur dioxide admixed with other gases. The hydrogen sulfide introduced through the line 213 mixes inside the reactor 221 with the sulfur dioxide introduced through the line flue gas (approximately 2100 F.,) passes from the sulfur burner via a line 141 to a waste heat boiler 142,

where aportionof its heat content is utilized in the generation of process steam. The flue gas passes from the boiler 142 at a substantially lower temperature (about 700 F.) via a line 143, the heat exchanger 119 and a cooler 144 en route to the inlet to the low-pressure sulfur dioxide absorber 134 via the line 135. Residue fiuegas is discharged from the absorber 134 via a line 145 and, being essentially nitrogen, is "ented to the atmosphere. c g

It will be noted that this illustration of the sulfur recovery system differs from certain of the others presented heretofore, since the concentrated sulfur-free organic solvent ilows first to the high-pressure sulfur dioxide absorber, thence to the low-pressure sulfur dioxide absorber to complete dissolution of this reactant, and is then pumpedto the reactor where the reaction takes placeand recoveryof elemental-sulfur is effected.

Example 3 I Another embodiment of this invention is shown in FIG. 11 in which system the acid gases produced by a large amine-type gas sweetening plant are processed for and 75%. carbon dioxide and which enters the sulfur recovery system at 10 p.s.i.g. and 100 F.

Referring to FIG. 11 acid'gas from an amine-type sweetening plant enters the sulfur recovery system via v a'lin'e' 211 connected to a three-way valve 212. At the 220. This mixture of gases passes upward through the reactor 221, contacting a descending stream of a suitable organic solvent, such as triethylene glycol, which may containsulfur particles and some sulfur dioxide in solution, Cool, concentrated sulfur dioxide-free solvent is pumped into thetop of the vessel 221 via anozzle 222 and the upper portion of vessel 221 serves as an absorber for unreacted sulfur dioxide which may tend to escape the reactor with the residue gas. In this instance, cool concentrated solvent is pumped into the absorber-reactor at a rate of approximately 140 gallons per minute so that the residue gas leaving the vessel.

via a line 223 is quite thoroughly dehydrated and denuded of sulfur dioxide. Proper control of operating conditions should produce an inert residue gas which might be processed for its carbon dioxide content or usedfor other purposes where an inert, dry gas is required.

Sulfur-laden solvent accumulating in the base of the reactor 221 flows to a slurry decanter and melt tank 225 via a line 224. Here the slurry is heated to 250275 F.

particles melt, agglomerate and settle into the lower, molten sulfur phase while the solvent rises to form the upper layer. Any dissolved gases such as sulfur dioxide are stripped from solution and are discharged back to the reactor 221 via a line 227. Molten sulfur is withdrawn from the system and run to storage via a line 228' while decanted solvent is withdrawn from the melt tank 225 via a. line 229, picks up heat in exchangers 230 and is discharged into a solvent still 232 via a line 231. Here, the liquid portion of the feed descends the still and is contacted by rising vapors, principally steam, to the extent that excess water is stripped from solution and passes overhead from the still 232 via a vapor line 233, a condenser 234 and accumulates in a reflux drum 235. Such water as may be required for refluxipasses to a reflux pump 237 via a line 236 whence it is lifted via a line 238 and discharged into the top of the still 232 via a nozzle 239. Proper use of water as reflux prevents the loss of excessive quantities of solvent in the still overhead. Excess water from the reflux drum 235 may be treated and used, or wasted as circumstances require.

valve 212, the acid gas is split into two streams. The

stream entering line 213 is twice the size of the-stream Noncondensible gases are vented from the reflux drum 235 via a line 240. Y

Solvent descending the still 232 accumulates on a chimney tray 2.41 and passes to twin reboilers 243 via lines 242. Here the solvent temperature is raised to the desired level, such as approximately 400 F. for triethylene glycol, and any vapors so generated are vented from the reboilers 243 via line 244 and discharged into the lower portion of the still 232 whence they pass upward through 19 the chimney tray 241 to contact the descending solvent stream.

Hot solvent is withdrawn from the base of the still 232 via a line 245 en route to a hot solution pump 246. S01- vent discharged from the pump 246 may pass either into the heating element 226 of the melt tank 225 via a line 247, or may be diverted by a valve 248, under control of a recording temperature controller 249 installed in the melt tank 225, to the heat exchangers 230 via a line 250. Emerging from the heat exchangers 230, the cooler solvent passes to a tubular cooler section 252, located in the lower portion of a cooling tower 253, via line 251. Here the solvent is cooled to approximately 100 F. and is directed to the upper portion of the absorber-reactor vessel 221, entering at the nozzle 222 via a line 254.

Cooling water from the basin of the cooling tower 253 is pumped over the tower by a pump 255 which may, if required, pump a portion of this water through reactor intercoolers 256 and 257 located in the absorberreactor 221. By this means, control of reactor temperatures may be accomplished at a level which favors the reactions therein.

The system described here should produce approximately 38 long tons of sulfur per day and 5000M cf. of dry, inert residue gas whose composition is approximately 60% carbon dioxide and 40% nitrogen with trace of oxygen. In addition, operation of the process will produce about 6500 gallons of water which might be utilized to good advantage in areas where water is scarce. Energy requirements approximate 150 brake horsepower for pumps and compressors and 170M c.f. per day of fuel gas for reboiler service.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

l. Apparatusfor the removal of hydrogen sulfide from gas containing the same, which comprises the combination of a reaction chamber for contacting said gas with sulfur dioxide in the presence of an organic solvent to induce reaction between hydrogen sulfide and sulfur dioxide whereby sulfur and water are formed, a lower inlet connection for said gas into said reaction chamber, an upper inlet connection for a solution of said sulfur dioxide in a first portion of said organic solvent into said reaction chamber, mixing means within said reaction chamber to effect contact between said sour gas, said sulfur dioxide and said first portion of said organic solvent, 21 first absorber chamber for contacting treated gas from the reactor chamber with a second portion of said organic solvent to absorb and remove sulfur dioxide from said treated gas and communicating with said reaction chamber to cycle gas between said reaction chamber and said first absorber chamber, an outlet connection for treated gas at the top of said first absorber chamber, an inlet connection-near the top of said first absorber chamber for introduction of said second portion of said organic solvent, an outiet connection for said organic solvent containing water and sulfur from the bottom of said reaction chamber, means for heating said organic solvent containing water and sulfur to a temperature above the melting point of sulfur to liquify and coagulate said sulfur, means for separating said liquified sulfur from said organic solvent containing water, still means for drying said organic solvent by heating it to a temperature whereat the water contained therein is evaporated, a second absorber chamber, means for cycling saiddried organic solvent to said second absorber chamber, an inlet connection near the top of said second absorber chamberwherein the organic solvent is introduced and descends countercurrent to a stream of sulfur dioxide gas and is removed from the bottom of said second absorber chamber through an outlet connection, an inlet connection for sulfur dioxide near the bottom of said second absorber chamber, pumping means for transferring said organic solvent containing sulfur dioxide from'the 20 outlet of said second absorber chamber to the upper inlet connection into said reaction chamber.

2. Apparatus as defined in claim 1 wherein the lower inlet connection into said second absorber chamber is connected to a sulfur burner so as to provide a source of sulfur dioxide to said second absorber chamber, said sulfur burner being in turn connected to said sulfur removal means to provide means for transporting a part of the separated sulfur to the sulfur burner for oxidation to sulfur dioxide.

3. Apparatus for the removal of hydrogen sulfide and nitrogen from gas containing the same, which comprises the combination of a reaction chamber for contacting said gas with sulfur dioxide in the presence of an organic solvent to induce reaction between hydrogen'sulfide and sulfur dioxide to form sulfur and water, means for supplying organic solvent to said reaction chamber, a first absorber chamber communicating with said reaction chamber for contacting treated gas with liquid sulfur dioxide to absorb nitrogen therefrom and for passage of solvent between said absorber chamber and said reactor chamber, means for supplying liquid sulfur dioxide to said first absorber chamber, a second absorber chamber connected to said first absorber chamber for contacting treated gas with said organic solvent to remove sulfur dioxide therefrom, means connected to said reaction chamber for separating sulfur from organic solvent and water, means for recycling organic solvent to said absorber and reaction chambers, means connected to said first absorber chamber for separating nitrogen from the liquid sulfur dioxide, and means for recycling liquid sulfur dioxide to said reactor and first absorber chambers.

4. Apparatus for the removal of hydrogen sulfide and nitrogen from gas containing the same, which comprises the combination of a reaction chamber for contacting said gas with sulfur dioxide in the presence of an organic solvent to induce reaction between hydrogen sulfide and sulfur dioxide to form sulfur and water, means for sup plying organic solvent to said .reaction chamber, a first absorber chamber communicating with said reaction chamber for contacting treated gas with liquid sulfur dioxide to absorb nitrogen therefrom and for passage of solvent be tween said absorber chamber and said reactor chamber, means for supplying liquid sulfur dioxide to said first absorber chamber, a second absorber chamber connected to said first absorber chamber for contacting treated gas with said organic solvent to remove sulfur dioxide therefrom, means connected to said reaction chamber for separating sulfur from organic solvent and water, means for recycling organic solvent to said absorber and reaction chambers, refrigeration means connected to said first absorber chamber for separating nitrogen from the liquid sulfur dioxide, and means for recycling liquid sulfur dioxide to said reactor and first absorber chamberst 5. Apparatus for the removal of hydrogen sulfide and nitrogen from gas containing the same, which compris s the combination of a reaction chamber for contacting said gas with sulfur dioxide in the presence of an org n solvent to induce reaction between hydrogen sulfid and sulfur dioxide to form sulfur and water, means for supplymg organic solvent to said reaction chamber, a first absorber chamber communicating with said reaction chamber for contacting treated gas with liquid sulfur dioxide to absorb nitrogen therefrom and for passage of solvent between said absorber chamber and said reactor chamber, means for supplying liquid sulfur dioxideto said first absorbet chamber, a second absorber chamber connected to sa d first absorber chamber for contacting treated gas with said organic solvent to remove sulfur dioxide therefrom, means connected to said reaction chamber for separating sulfur from organic solvent and water, means for recycling: organic solvent to said absorber and reaction chambers, refrigeration means connected to said first absorber cham-- ber for separating nitrogen from the liquid sulfur dioxide, means for removing sulfur dioxide gas from the nitrogengas, and means for recycling liquid su fur dioxide to said reactor and first absorber chambers.

6. Apparatus for the removal of hydrogen sulfide and nitrogen from gas containing the same, which comprises solvent to induce reaction between hydrogensulfide and sulfur dioxide to form sulfur and water, means for supplying organic solvent to said reaction chamber, a first absorber chamber communicating with said reaction chamber for contacting treated gas with liquid sulfur dioxide to absorb nitrogen therefrom and for passage of solvent between said absorber chamber and said reactor chamber, means for supplying liquid sulfur dioxide to said first absorber chamber, a second absorber chamber con nected to said first absorber chamber for contacting treated gas with said organic solvent to remove sulfur dioxide therefrom, means connected to said reaction chamber for separating sulfur from organic solvent and water, means for dehydrating and recycling organic solvent to said absorber and reaction chambers, refrigeration means connected to said first absorber chamber for separating nitrogen from the liquid sulfur dioxide, means for removing sulfur dioxide gas from the nitrogen gas, and means for recycling liquid sulfur dioxide to said reactor and first absorber chambers.

7. Apparatus for the removal of hydrogen sulfide and nitrogen from gas containing the same, which comprises the combination of a reaction chamber for contacting said gas with liquid sulfur dioxide and an organic solvent to induce reaction between hydrogen sulfide and part of the sulfur dioxide to form sulfur and water and to remove nitrogen from said gas by absorption by the remainder of the liquid sulfur dioxide, means for supplying liquid sulfur dioxide and organic solvent to said reaction chamher, an absorber chamber communicating with said reactor'chamber for contacting treated gas with said organic solvent to absorb sulfur dioxide therefrom and for passage of solvent between said absorber chamber and said reactor chamber, means for supplying organic solvent to said absorber chamber, means connected to said reaction chamber for separating sulfur from organic solvent and water, means for dehydrating and recycling organic solvent to said absorber and reaction chambers, means connected to said absorber chamber for separating nitrogen gas from liquid sulfur dioxide, means for removing sulfur dioxide gas from the nitrogen gas, and means for recycling liquid sulfur dioxide to saidreactor and absorber chambers.

8. Apparatus for the removal of hydrogen sulfide from gas containing the same comprising means for contacting said gas with sulfur dioxide in the presence of an organic solvent to induce reaction between the hydrogen sulfide and sulfur dioxide to form sulfur and water, inlet means to the first-mentioned means for said gas, sulfur dioxide and organic solvent mixing means within said first-mentioned means, means communicating with said first-mentioned means for contacting treated gas with said organic solvent to absorb sulfur dioxide therefrom and for passage of solvent between said absorber chamber and said reactor chamber, outlet means for treated gas from the last above mentioned means, inlet means to said last above-mentioned means for organic solvent near the top of said last above-mentioned means, outlet means for organic solvent containing water and sulfur from said last above-mentioned means, means communicating with said last abovementioned means for cycling organic solvent to said firstmentioned means and to said last above-mentioned means.

References Cited in the file of this patent UNITED STATES PATENTS 2,177,068 Hutchinson Oct. 24, 1939 2,370,020 Doumani Feb. 20, 1945 2,445,468 Blohn July 20, 1948 2,772,146 Peppig Nov. 27, 1956 2,881,047 Townsend Apr. 7, 1959 2,992,076 Thompson et al July 11, 1961 2,998,304 Urban et a1 Aug. 29, 1961 

1. APPARATUS FOR THE REMOVAL OF HYDROGEN SULFIDE FROM GAS CONTAINING THE SAME, WHICH COMPRISES THE COMBINATION OF A REACTION CHAMBER FOR CONTACTING SAID GAS WITH SULFUR DIOXIDE IN THE PRESENCE OF AN ORGANIC SOLVENT TO INDUCE REACTION BETWEEN HYDROGEN SULFIDE AND SULFUR DIOXIDE WHEREBY SULFUR AND WATER ARE FORMED, A LOWER INLET CONNECTION FOR SAID GAS INTO SAID REACTION CHAMBER, AN UPPER INLET CONNECTION FOR A SOLUTION OF SAID SULFUR DIOXIDE IN A FIRST PORTION OF SAID ORGANIC SOLVENT INTO SAID REACTION CHAMBER, MIXING MEANS WITHIN SAID REACTION CHAMBER TO EFFECT CONTACT BETWEEN SAID SOUR GAS, SAID SULFUR DIOXIDE AND SAID FIRST PORTION OF SAID ORGANIC SOLVENT, A FIRST ABSORBER CHAMBER FOR CONTACTING TREATED GAS FROM THE REACTOR CHAMBER WITH A SECOND PORTION OF SAID ORGANIC SOLVENT TO ABSORB AND REMOVE SULFUR DIOXIDE FROM SAID TREATED GAS AND COMMUNICATING WITH SAID REACTION CHAMBER TO CYCLE GAS BETWEEN SAID REACTION CHAMBER AND SAID FIRST ABSORBER CHAMBER, AN OUTLET CONNECTION FOR TREATED GAS AT THE TOP OF SAID FIRST ABSORBER CHAMBER, AN INLET CONNECTION NEAR THE TOP OF SAID FIRST ABSORBER CHAMBER FOR INTRODUCTION OF SAID SECOND PORTION OF SAID ORGANIC SOLVENT, AN OUTLET CONECTION FOR SAID ORGANIC SOLVENT CONTAINING WATER AND SULFUR FROM THE BOTTOM OF SAID REACTION CHAMBER, MEANS FOR HEATING SAID ORGANIC SOLVENT CONTAINING WATER AND SULFUR TO A TEMPERATURE ABOVE THE MELTING POINT OF SULFUR TO LIQUIFY AND COAGULATE SAID SULFUR, MEANS FOR SEPARATING SAID LIQUIFIED SULFUR FROM SAID ORGANIC SOLVENT CONTAINING WATER, STILL MEANS FOR DRYING SAID ORGANIC SOLVENT BY HEATING IT TO A TEMPERATURE WHEREAT THE WATER CONTAINED THEREIN IS EVAPORATED, A SECOND ABSORBER CHAMBER, MEANS FOR CYCLING SAID DRIED ORGANIC SOLVENT TO SAID SECOND ABSORBER CHAMBER, AN INLET CONNECTION NEAR THE TOP OF SAID SECOND ABSORBER CHAMBER WHEREIN THE ORGANIC SOLVENT IS INTRODUCED AND DESCENDS COUNTERCURRENT TO A STREAM OF SULFUR DIOXIDE GAS AND IS REMOVED FROM THE BOTTOM OF SAID SECOND ABSORBER CHAMBER THROUGH AN OUTLET CONNECTION, AN INLET CONNECTION FOR SULFUR DIOXIDE NEAR THE BOTTOM OF SAID SECOND ABSORBER CHAMBER, PUMPING MEANS FOR TRANSFERRING SAID ORGANIC SOLVENT CONTAINING SULFUR DIOXIED FROM THE OUTLET OF SAID SECOND ABSORBER CHAMBER TO THE UPPER INLET CONNECTION INTO SAID REACTION CHAMBER. 